1. Field of the Invention
The present invention relates to a conductive thermoplastic elastomer composition, a method of producing the conductive thermoplastic elastomer composition, and a molding formed by processing the conductive thermoplastic elastomer composition. More particularly, the present invention relates to a conductive thermoplastic elastomer composition which is effectively used as a conductive roller for use in an image-forming apparatus such as a copying machine, a printer, a facsimile, and the like.
2. Description of the Related Art
As methods of imparting conductivity to an elastomer, the following two methods are conventionally used: In one known method, an electroconductive polymer composition containing a conductive filler such as powder of metal oxide, carbon black or the like in a polymer thereof is used. In the other known method, an ionic-conductive polymer composition such as urethane rubber, acrylonitrile butadiene rubber, epichlorohydrin rubber or the like is used.
In the case where the electroconductive polymer composition is used to compose a conductive roller, there is a region in which an electric resistance changes rapidly owing to a slight change of the addition amount of the conductive filler. Thus it is very difficult to control the electric resistance of the conductive roller. In addition, because it is difficult to uniformly disperse the conductive filler in the polymer, an electric resistance value has variations in the circumferential and widthwise directions of the conductive roller.
The electric resistance value of the conductive roller using the electroconductive polymer composition depends on a voltage applied thereto. In particular, in the case where the carbon black is used as the conductive filler, the electric resistance value of the conductive roller depends greatly on the voltage applied thereto. Further when the electroconductive polymer composition contains a very large amount of the conductive filler such as the carbon black, it is difficult to mold the electroconductive polymer composition.
The conductive roller using the electroconductive polymer composition has the above-described problems. In recent years, a high-quality image forming technique including a digital image processing technique and color image processing technique is outstanding. Thus there is a tendency that the ionic-conductive polymer composition is used preferentially to the electroconductive polymer composition.
Most of the ionic-conductive polymer composition used to form the conductive roller consists of a vulcanized rubber composition. But the vulcanized rubber composition is not thermoplastic and cannot be recycled.
Such being the case, an ionic-conductive polymer which is thermoplastic and can be recycled has come to be used. Above all, the conductive roller using epichlorohydrin rubber has a low electric resistance value and preferable properties. But in some cases, the ionic-conductive thermoplastic elastomer such as the epichlorohydrin rubber containing chlorine generates a toxic gas such as hydrogen chloride and dioxine when it is discarded.
In Japanese Patent Application Laid-Open No. 8-183866, there is disclosed the sheet-shaped thermoplastic elastomer composed of the olefin thermoplastic elastomer to which the permanent antistatic agent is added. The sheet-shaped thermoplastic elastomer can be recycled. Further because the olefin thermoplastic elastomer does not contain chlorine, the sheet-shaped thermoplastic elastomer does not pollute environment when it is discarded. In addition, a thermoplastic elastomer of a bleeding type containing the conductive plasticizer as the antistatic agent is also disclosed.
The permanent antistatic agent contained in the sheet-shaped thermoplastic elastomer is capable of decreasing the surface electric resistance value thereof, but does not decrease the volume resistivity thereof and causes the electric resistance thereof value to become high. Further the sheet-shaped thermoplastic elastomer has a high compression set. Thus a conductive roller composed of the sheet-shaped thermoplastic elastomer does not have favorable properties.
The thermoplastic elastomer of the bleeding type has a low mechanical property and a high compression set. In addition the plasticizer contained in thermoplastic elastomer bleeds and greatly pollutes other parts such as a photoreceptor. Therefore the thermoplastic elastomer cannot be used as a component part of an image-forming apparatus such as a copying machine, a printer, and the like.
The present applicant developed conductive thermoplastic elastomers having a semiconductive electric resistance value and favorable mechanical properties, for example, a low compression set. More specifically, as disclosed in Japanese Patent Application Laid-Open No. 2004-189884 (patent document 2) and Japanese Patent Application Laid-Open No. 2004-272209 (patent document 3), the present applicant proposed the conductive thermoplastic elastomer containing the polymer represented by the polyether polymer and the conductive salt contained in the thermoplastic elastomer.
But there is room for improvement in the conductive thermoplastic elastomer so that it enhances the dispersibility of the components thereof to a higher extent and prevents the properties thereof from being deteriorated and the conductive thermoplastic elastomer from defectively molded owing to the insufficient dispersibility of the components thereof.
Disclosed in Japanese Patent Application Laid-Open No. 2004-189883 (patent document 4) is the compatibilizing agent containing at least one of the acid-modified EPDM and the acid-modified hydrogenated styrene thermoplastic elastomer to finely disperse the polyamide resin in the dynamically crosslinked thermoplastic elastomer. But in the patent document 4, investigations were not made on whether the compatibilizing agent is effective for finely dispersing components, other than the polyamide resin, such as the conductive salt in the thermoplastic elastomer. In the patent document 4, no description or suggestion was made on compatibilizing agents other than the above-described compatibilizing agent.
Japanese Patent Application Laid-Open No. 8-183866
Japanese Patent Application Laid-Open No. 2004-189884
Japanese Patent Application Laid-Open No. 2004-272209
Japanese Patent Application Laid-Open No. 2004-189883